I'm not quite sure what you mean by the "domain name" of a user. The domain name is a property of the Active Directory server, not of the user. Do you mean the user name? In which case, userPrincipalName is probably what you want. Here's a
list of User object attributes, although you might find Microsoft's documentation more useful, especially the
User class page and the
User Object attributes page and more specifically, the
User naming attributes page.